1. Field of the Invention
The present invention relates to a webbing retractor, and in particular, to a webbing retractor which permits pulling-out of a webbing and absorbs energy at the time when pulling-out of the webbing is impeded.
2. Description of the Related Art
In a webbing retractor, rotation of a spool (take-up shaft) in a webbing pull-out direction is locked at the time the vehicle rapidly decelerates, such that pulling-out of the webbing is impeded. As the lock mechanism, a lock device is disposed in the vicinity of a device frame at one end side of the spool. Due to this lock mechanism being operated at the time the vehicle rapidly decelerates, rotation of the spool in the webbing pull-out direction is impeded.
Further, in such a webbing retractor, at the time that pulling-out of the webbing is impeded, pulling-out of a predetermined amount of the webbing is permitted so as to aim for energy absorption. An example of the energy absorbing mechanism is a structure in which a torsion bar is provided coaxially with the spool. Generally, one end portion of a torsion bar is connected to the spool so as not to rotate relatively thereto. The other end portion of the torsion bar is connected to a lock base, which is connected to a lock mechanism, such that this other end portion does not rotate relatively to the lock base. Usually, the spool and the lock base rotate integrally via the torsion bar. However, in a state in which rotation of the lock base in the webbing pull-out direction is impeded at the time when the vehicle rapidly decelerates, the spool rotates in the webbing pull-out direction with respect to the lock base due to the tensile force of the webbing. At this time, the torsion bar twists such that energy is absorbed, and a predetermined amount of rotation of the spool is permitted.
Moreover, an example of a stopper device for limiting, to a predetermined amount, the amount of rotation of the spool which accompanies energy absorption is a structure which is provided with a lock nut which screws together with the outer peripheral portion of the lock base and which is moved in the axial direction by rotating integrally with the spool. When the lock nut abuts the end surface of the lock base such that movement of the lock nut in the axial direction is impeded, further rotation of the spool is impeded.
However, in such a conventional webbing retractor, there are the problems that the structure of the stopper device is complex, and the assembly processes are complicated and expensive.
Further, for example, in a vehicle equipped with an air bag device, it is preferable to provide a gradually changing device by which the load applied to the vehicle occupant from the webbing in the energy absorbing process (i.e., the force limiter load) is gradually reduced, so as to suppress the total load applied to the vehicle occupant from the air bag device and the webbing. However, in a webbing retractor such as that described above, the force limiter load is a constant value due to the properties of the material of the torsion bar and the dimensions and configuration of the torsion bar. It is difficult to gradually decrease the force limiter load (i.e., to provide a gradually changing device).
In view of the aforementioned, an object of the present invention is to provide a webbing retractor whose structure is simple, and which can limit the webbing pull-out amount at the time of energy absorption, and which can reduce the force limiter load in the energy absorbing process.
In order to achieve the above object, a webbing retractor of the present invention comprises: a spool on which a webbing is taken-up and from which a webbing is pulled-out; a rotating member provided so as to be coaxial with the spool and so as to be rotatable relative to the spool, the rotating member usually rotating integrally with the spool, and in predetermined cases, rotation of the rotating member in a webbing pull-out direction is impeded; an elongated member whose one end portion is fixed to one of the spool and the rotating member, and whose intermediate portion is engaged with another of the spool and the rotating member, and when rotation of the rotating member in the webbing pull-out direction is impeded, accompanying relative rotation of the spool and the rotating member, the elongated member is rubbed or drawn at an engaged region thereof; and stopper device provided at the other of the spool and the rotating member so as to abut the intermediate portion of the elongated member, and when, accompanying relative rotation of the spool and the rotating member, a state of abutment of the stopper device with the elongated member is cancelled, the stopper device impedes relative rotation, in the webbing pull-out direction, of the spool with respect to the rotating member.
In the webbing retractor, because the rotating member usually rotates integrally with the spool, the webbing is freely taken-up and pulled-out. At this time, because no relative rotation arises between the spool and the rotating member, the stopper device does not operate.
In a predetermined case such as, for example, when the vehicle rapidly decelerates or the like, when rotation of the rotating member in the webbing pull-out direction is impeded, relative rotation arises between the rotating member and the spool to which tensile force of the webbing is applied and which is rotated in the webbing pull-out direction. Accompanying this relative rotation, the elongated member is rubbed. The accompanying drawing load is applied as force limiter load, and energy absorption is thereby achieved.
Further, when, accompanying the relative rotation, the state of abutment of the elongated member and the stopper device is cancelled, the stopper device is operated such that relative rotation of the spool in the webbing pull-out direction with respect to the rotating member is impeded. At this time, because rotation of the rotating member in the webbing pull-out direction is impeded, rotation of the spool in the webbing pull-out direction is impeded, and further pulling out of the webbing is restricted.
Here, the elongated member is merely fixed to one of the spool and the rotating member and engaged to the other of the spool and the rotating member. Operation of the stopper device is restricted merely by the stopper device being abutted by the intermediate portion of the elongated member. (Namely, the elongated member, which serves as an energy absorbing member, also works as a trigger for operating the stopper device.) Thus, the structure is simple. Further, by providing these components at the outer side of one end of the spool, there is no need to assemble lock nuts or the like in the interior of the spool as in the conventional art, and the assembly process as well is simplified.
In this way, in the webbing retractor, the structure is simple, the pulled-out amount of the webbing at the time of energy absorption can be limited.
For example, a rotation impeding device which is structured so as to include a driving device, which is operated when an acceleration sensor detects a predetermined acceleration, and a pawl, which is connected to the drive device and which, when the drive device is operated, engages with a lock tooth formed at the outer peripheral portion or the like of the rotating member, may be used as the device for impeding rotation of the rotating member in the webbing pull-out direction in predetermined cases.
In the webbing retractor, preferably, the elongated member is disposed between an outer peripheral portion of the one of the spool and the rotating member and an inner peripheral portion of the other of the spool and the rotating member which outer peripheral portion and inner peripheral portion oppose one another, and accompanying relative rotation of the spool and the rotating member, the elongated member is taken-up onto the outer peripheral portion of the one of the spool and the rotating member.
In the above-mentioned webbing retractor, the elongated member is provided between the outer peripheral portion of one of the spool and the rotating member and the inner peripheral portion of the other of the spool and the rotating member, which outer peripheral portion and inner peripheral portion oppose one another. Thus, the elongated member can be made compact by being formed, for example, in a circular arc shape or a coiled form, and the degrees of freedom in setting the length of the elongated member (the amount of rotation of the spool which is permitted at the time of energy absorption) are increased.
The elongated member is taken-up on the outer peripheral surface of the one of the spool and the rotating member to which one end portion of the elongated member is fixed. Thus, in the energy absorbing process, the direction of pulling at the region which is engaged with the other of the spool and the rotating member is substantially constant, and a stable rubbing force (force limiter load) can be obtained. In particular, if the fixed region of the one end portion of the elongated member is disposed such that the phase thereof in the direction of relative rotation is ahead of that of the engaged region so that the elongated member take-up direction in the initial stages substantially coincides with the direction of a tangent line connecting the engaged region and the outer peripheral surface, the pulling direction is always substantially constant from the initial stages of energy absorption, and such a structure is even more suitable.
In this way, in the webbing retractor, the structure is even more simple, the pulled-out amount of the webbing at the time of energy absorption can be limited, and the force limiter load is stable.
In the webbing retractor, more preferably at the elongated member, a sectional area of the intermediate portion which is rubbed or drawn at least at the engaged region decreases gradually toward another end portion of the elongated member.
In the above-mentioned webbing retractor, the sectional area of the rubbed portion of the elongated member, which moves relative to the engaged region as the spool and the rotating member rotate relatively, gradually decreases from the fixed one end portion toward the other end portion. Thus, the force limiter load in the energy absorbing process gradually decreases.
In this way, in the above-mentioned webbing retractor, the structure is simple, the pulled-out amount of the webbing at the time of energy absorption can be limited, and the force limiter load in the energy absorbing process is reduced.
Preferably, any of the above-mentioned webbing retractors further comprises: a lock base provided at one end side of the spool so as to be coaxial with the spool and so as to be able to rotate relatively with respect to the spool, and when one of a rapid deceleration of a vehicle and rapid pulling-out of a webbing is sensed, rotation of the lock base in the webbing pull-out direction is impeded by a locking device; and a torsion bar provided within the spool and coaxially with the spool, one end portion of the torsion bar being connected to the spool and another end portion of the torsion bar being connected to the lock base, the torsion bar usually being made to rotate integrally with the spool and the lock base, and when rotation of the lock base in the webbing pull-out direction is impeded, the torsion bar, while twisting due to tensile force of the webbing, rotates the spool in the webbing pull-out direction relatively to the lock base.
In the above-mentioned webbing retractor, as the energy absorbing member, a torsion bar is provided in addition to the elongated member. At the time when a rapid deceleration of the vehicle or rapid pulling-out of the webbing is sensed, when the rotation of the lock base in the webbing pull-out direction is impeded by the locking device, the torsion bar, while twisting, permits rotation of the spool in the webbing pull-out direction. The twisting load of the torsion bar is added to the force limiter load.
Thus, the elongated member can be made compact, the respective energy absorbing members can be arranged in a well-balanced manner within the webbing retractor, and the webbing retractor can, on the whole, be made compact and lightweight. Further, as compared with a structure, in which energy absorption is carried by only a torsion bar as in the conventional art, a stopper device and a gradually changing device can be obtained with a simple structure.
Moreover, for example, if a structure is provided in which the rotation of the rotating member in the webbing pull-out direction can be impeded at arbitrary times (i.e., if a structure is provided in which the predetermined cases can be set separately from the time of operating the locking device), a different force limiter load can be selected in advance or in the energy absorbing process.
In this way, in the above-mentioned webbing retractor, the structure is simple, the pulled-out amount of the webbing at the time of energy absorption can be limited, the force limiter load in the energy absorbing process is reduced, and the webbing retractor is made to be compact.
In the webbing retractor, more preferably, the lock base also functions as the rotating member.
In the above-mentioned webbing retractor, when rotation of the lock base in the webbing pull-out direction is impeded, the torsion bar, to which the tensile force of the webbing is applied, twists, and the spool and the lock base rotate relatively. Accompanying this relative rotation, the elongated member is rubbed, and the torsion bar and the elongated member simultaneously operate as energy absorbing members, and energy absorption is achieved. Thus, the amount of rotation of the spool (the pull-out amount of the webbing) which is permitted at the time of energy absorption can always be maintained constant.
Here, because the lock base also serves as the rotating member, the number of parts can be reduced (the rotating member itself and the mechanism for impeding rotation of the rotating member in the webbing pull-out direction can be eliminated). The structure becomes more simple, the assembly process becomes more simple, and the webbing retractor can be made compact and lightweight.
In this way, in the above-mentioned webbing retractor, the structure is even more simple, and the webbing pull-out amount at the time of energy absorption can be reliably limited. Further, the force limiter load in the energy absorbing process is reduced, and the webbing retractor is made to be even more compact.